Syria said four coalition jets killed three soldiers and wounded 13 in the eastern Deir al-Zor province on Sunday evening, calling it an act of aggression, the first time it has made such an accusation.

Any such strike by US-led coalition planes, which have been focussing their fire on Islamic State militants, would further complicate an increasingly regional conflict now nearly five years old.

The Syrian Observatory for Human Rights monitoring group reported earlier that jets likely to be from the coalition hit part of the Saeqa military camp near the town of Ayyash in Deir al-Zor province, killing four Syrian army personnel.

But a US military official, speaking on condition of anonymity, said the United States is certain that Russia was responsible for the deadly strike on the Syrian army camp.

A US defence official, who declined to be named, dismissed the idea that the coalition would target the Syrian military.

Another US defence official said Deir al-Zor was among the locations Russia had targeted on Sunday. Russian officials were not immediately available for comment.

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